The present invention relates to calcium-iron oxide composite particles. More particularly, the present invention relates to calcium-iron oxide composite particles, a hydrogen chloride-scavenger comprising the calcium-iron oxide composite particles, which is capable of effectively capturing harmful hydrogen chloride generated by thermal decomposition or combustion of chorine-containing resin molded products upon fire or incineration thereof, and fixing the hydrogen chloride as stable calcium chloride or the like.
The chlorine-containing resin molded products according to the present invention can be used as interior and exterior building materials such as blinds, wall papers, flooring materials, outer walls or tubs; materials for transportation means such as automobiles, vehicles, ships or airplanes; structural materials for machineries, equipments, apparatuses, etc.; agricultural materials for greenhouse culture of agricultural products, etc.; or materials for various other application fields.
Chlorine-containing resins such as polyvinyl chloride, polyvinylidene chloride or chlorinated polyethylene which are generally used as raw materials for molded resin products, have been mass-produced and widely used in various application fields because of inexpensiveness and excellent processability thereof. In particular, in Japan, polyvinyl chloride have been currently mass-produced in an amount as large as about 2,300,000 tons a year.
However, when resin molded products composed of such chlorine-containing resins are burnt upon fire or used resin molded products are incinerated, the chlorine-containing resins are thermally decomposed by heating, so that a large amount of harmful hydrogen chloride derived from chlorine in the resins is generated. Consequently, such chlorine-containing resin molded products has caused significant social problems such as damage to human bodies and other organisms or environmental pollution, e.g., air pollution.
On the other hand, from the standpoints of safety, hygiene or environmental protection, it has been studied to replace the chlorine-containing resin molded products with resin molded products containing no chlorine. However, with increase in amount of caustic soda (sodium hydroxide) produced, since a large amount of chlorine gas has been generated and the large amount of chlorine-containing resins has been also produced, it is not easy to replace the chlorine-containing resin molded products with other resin molded products containing no chlorine.
In consequence, it has been strongly demanded to provide a chlorine-containing resin molded product which can be sufficiently prevented from generating harmful hydrogen chloride even upon fire or incineration.
Hitherto, hydrogen chloride generated from the chlorine-containing resin molded products upon combustion or incineration thereof, have been treated and removed by a method of absorbing hydrogen chloride into slaked lime due to the reaction therebetween, a method of neutralizing hydrogen chloride with caustic soda, or the like.
There is also known a method of adding calcium carbonate the chlorine-containing resin composition is thermally decomposed and converted into a liquid fuel, and reacting the calcium carbonate with hydrogen chloride generated upon the thermal decomposition, thereby fixing the hydrogen chloride as calcium chloride (Japanese Patent Application Laid-open (KOKAI) No. 56-122894(1981)).
Further, there is known a method of removing hydrogen chloride by allowing calcium carbonate particles and iron oxide particles to co-exist upon incineration of the chlorine-containing resins, the calcium carbonate particles and the iron oxide particles being granulated with an organic binder (Japanese Patent Application Laid-open (KOKAI) No. 8-82411(1996)).
Further, there is known a method of burning combustible wastes at a temperature of not less than 850xc2x0 C. under the co-existence of calcium compound particles and iron oxide particles, thereby removing hydrogen chloride generated (Japanese Patent Application Laid-open (KOKAI) No. 8-270924(1996)).
Furthermore, there is known a chlorine-containing resin composition produced by blending a hydrogen chloride-scavenger composed of lithium carbonate particles or the like and iron oxide particles with a chlorine-containing resin, wherein the dehydrochlorination reaction by the hydrogen chloride-scavenger is promoted by catalytic action of the iron oxide particles (Japanese Patent Application Laid-open (KOKAI) No. 9-241458(1997)).
More specifically, in Japanese Patent Application Laid-open (KOKAI) No. 9-241458(1997), there has been described a chlorine-containing resin composition produced by blending at least one kind of carbonate particles selected from the group consisting of lithium carbonate, sodium carbonate and magnesium carbonate, and iron oxide particles into a chlorine-containing resin, so that the amount of the carbonate particles is not more than one equivalent based on chlorine in the resin, and the amount of the iron oxide particles is 1 to 10% by weight based on the weight of the carbonate particles.
However, the above-mentioned prior arts have the following problems.
That is, in the case of the reacting and absorbing method using slaked lime or the neutralizing and washing method using caustic soda, hydrogen chloride is not suppressed from being generated, but the hydrogen chloride already generated is treated subsequently. Therefore, in particular, damages to human bodies and other organisms upon fire or environmental pollution cannot be inhibited.
Further, in the case of the reacting and absorbing method, an efficiency of the reaction between hydrogen chloride and slaked lime is low, so that in order to achieve an effective chlorine-fixativity, it is necessary that the slaked lime is used in such a large amount at least three times the theoretical equivalent required for the reaction with hydrogen chloride, thereby causing problems such as increase in treating costs.
In addition, since unreacted slaked lime contains dioxin showing a strong toxicity, there is caused such a disadvantage that the unreacted slaked lime must be converted into harmless substances before disposal. Further, expensive facilities are required to uniformly disperse the slaked lime.
In the method described in Japanese Patent Application Laid-open (KOKAI) No. 56-122894(1981), hydrogen chloride cannot be sufficiently inhibited from being generated. Further, in this method, the efficiency of reaction between hydrogen chloride and calcium carbonate is low, so that in order to achieve an effective chlorine-fixativity, it is necessary that the calcium carbonate is used in such a large amount at least five times the theoretical equivalent required for the reaction with hydrogen chloride, thereby causing problems such as the increase in treating costs.
In the methods described in Japanese Patent Application Laid-open (KOKAI) Nos. 8-82411(1996) and 9-241458(1997) in which a hydrogen chloride-scavenger composed of carbonate particles such as calcium carbonate particles or lithium carbonate particles and the iron oxide particles are mixed and blended with the chlorine-containing resin, when the temperature is excessively increased upon heating, the decomposition reaction such as dehydrochlorination reaction or polyene-forming reaction is accelerated at a part of the chlorine-containing resin by catalytic action of the iron oxide particles, thereby causing problems such as deterioration in quality and properties of the resin accompanying with discoloration thereof, etc.
Further, in the methods described in Japanese Patent Application Laid-open (KOKAI) Nos. 8-82411(1996), 8-270924(1996) and 9-241458(1997), hydrogen chloride-capturing reaction by the hydrogen chloride-scavengers is accelerated by the catalytic action of the iron oxide particles, thereby preventing the generation of hydrogen chloride to some extent. However, the generation of hydrogen chloride cannot be sufficiently inhibited by these methods. In the method described in Japanese Patent Application Laid-open (KOKAI) No. 9-241458(1997), it is required to use expensive lithium carbonate particles or the like. Therefore, the method is industrially disadvantageous.
In view of the above-mentioned problems, it has been strongly demanded to provide a hydrogen chloride-scavenger capable of sufficiently capturing hydrogen chloride generated from chlorine-containing resin molded products upon fire or incineration thereof, and preventing the chlorine-containing resins from being deteriorated in quality and properties.
As a result of the present inventors"" earnest studies, it has been found that by allowing calcium-iron oxide composite particles having a BET specific surface area of 1 to 100 m2/g and an iron atom content of 1 to 50 moles based on 100 moles of calcium atom wherein not less than 50% of the iron atom forms a calcium-iron ferrite phase, to exist upon incineration of a chlorine-containing resin, harmful hydrogen chloride generated by thermal decomposition or combustion of the chlorine-containing resin can be effectively captured and fixed. The present invention has been attained on the basis of the finding.
It is an object of the present invention to provide calcium-iron oxide composite particles and a hydrogen chloride-scavenger comprising, which is capable of effectively capturing harmful hydrogen chloride generated by thermal decomposition or combustion of a chlorine-containing resin molded product upon fire or incineration thereof, and fixing the hydrogen chloride as stable calcium chloride or the like.
It is another object of the present invention to provide to a chlorine-containing resin composition capable of sufficiently preventing hydrogen chloride from being generated upon fire or incineration thereof, and showing hardly the deterioration in quality and properties when molded.
To accomplish the aim, in a first aspect of the present invention, there is provided calcium-iron oxide composite particles having a BET specific surface area of 1 to 100 m2/g and containing iron atom in an amount of 1 to 50 moles based on 100 moles of calcium atom, the iron atom of not less than 50% based on the total amount of iron atom contained in said calcium-iron oxide composite particles being bonded with calcium atom for forming a calcium-iron ferrite phase.
In a second aspect of the present invention, there is a hydrogen chloride-scavenger comprising calcium-iron oxide composite particles having a BET specific surface area of 1 to 100 m2/g and containing iron atom in an amount of 1 to 50 moles based on 100 moles of calcium atom, the iron atom of not less than 50% based on the total amount of iron atom contained in said calcium-iron oxide composite particles being bonded with calcium atom for forming a calcium-iron ferrite phase.